Within the TU/e Kat-1 collaboration, we aim to construct a full-stack hybrid quantum computer. At its core, our quantum processor consists of individually trapped Rubidium-85 atoms in optical tweezers, with qubit states encoded in the hyperfine splitting of the atomic ground state. In this poster, we briefly introduce neutral-atom quantum computing and present the redesign and initial characterization of our experimental plat form, developed to support mid-circuit measurements as a crucial first step towards quantum error correction (QEC). Key improvements include the design of a four-loop antenna configuration for driving global microwave transitions with arbitrary polarizations and increased homogeneity. In addition, we introduce an alignment-free dual-wavelength local addressing system. This system suppresses relative beam-pointing instabilities between the trapping and addressing beams, enabling us to locally apply stable differential Stark shifts. Together with the global microwaves, this enables local state shelving into the ground-state Zeeman levels, which in turn allows site-selective mid circuit measurements- an important step towards the realization of QEC on our platform.
Within the TU/e Kat-1 collaboration, we aim to construct a full-stack hybrid quantum computer. At its core, our quantum processor consists of individually trapped Rubidium-85 atoms in optical tweezers, with qubit states encoded in the hyperfine splitting of the atomic ground state. In this poster, we briefly introduce neutral-atom quantum computing and present the redesign and initial characterization of our experimental plat form, developed to support mid-circuit measurements as a crucial first step towards quantum error correction (QEC). Key improvements include the design of a four-loop antenna configuration for driving global microwave transitions with arbitrary polarizations and increased homogeneity. In addition, we introduce an alignment-free dual-wavelength local addressing system. This system suppresses relative beam-pointing instabilities between the trapping and addressing beams, enabling us to locally apply stable differential Stark shifts. Together with the global microwaves, this enables local state shelving into the ground-state Zeeman levels, which in turn allows site-selective mid circuit measurements- an important step towards the realization of QEC on our platform.
Within the TU/e Kat-1 team, we aim to realize an implementation of a full-stack hybrid quantum computer. At its core, our quantum processor is based on neutral rubidium-85 atoms confined in optical tweezers, with qubit states encoded in the hyperfine splitting of the ground state. Within this poster, we present our plans and initial results of an upgraded experimental setup aimed at achieving higher gate fidelities. Key improvements include the design of a new four-coil configuration for driving global microwave transitions with arbitrary polarization and increased homogeneity. In addition, we introduce an alignment-free, dual-wavelength local addressing system based on shared acousto-optical deflectors. This system suppresses beam-pointing instabilities between the addressing and trapping beams. Together, these developments are expected to enhance the robustness and fidelity of both our global and local qubit operations.
Over the past decade, quantum information science has progressed from few-qubit demonstrations to experiments with hundreds of qubits. Neutral atom processors based on individual atoms trapped in arrays of optical tweezers have emerged as a leading candidate due to their inherent scalability and flexible connectivity. Advanced protocols like measurement-based state preparation and quantum error correction, however, require efficient crosstalk-free mid-circuit operations for the readout, reset, and replenishment of a subset of qubits. In typical single-species atom arrays, where all atoms are identical and on-resonance, such operations necessitate complex overheads from single-site addressing, coherent transport, or shielding techniques, to mitigate the qubit decoherence induced from photons scattered by neighboring atoms. To address this challenge of engineering scalable quantum architectures compatible with efficient control techniques, we introduce and implement the first dual-species atom array platform, and explore new dynamics inaccessible in single-species arrays. In this approach, two atomic species are addressed independently due to the spectral separation between their control wavelengths. We engineer two-dimensional arrays from individual rubidium (Rb) and cesium (Cs) atoms in up to 512 optical tweezers, and show that the two species can be independently trapped, cooled, and imaged with state-of-the-art performance metrics. Harnessing this intrinsic crosstalk-free control, we establish the key primitives of mid-circuit readout, real-time processing and feed-forward, and coherent mid-circuit reloading. By integrating these capabilities, we realize in-sequence, real-time correction of correlated phase errors via a spectator qubit protocol. Next, we excite atoms to Rydberg states in the Förster regime, accessing hitherto unobserved enhanced interspecies Rydberg interactions, and program them to implement the first interspecies CNOT gate. We combine this multispecies entanglement with mid-circuit readout to achieve quantum non-demolition measurement of a Rb-qubit using an auxiliary Cs-qubit, circumventing physical qubit transport. Finally, leveraging the two qubit modalities, we present the first experimental demonstration of quantum cellular automata in atom arrays using only global addressing, and prepare a 17-qubit Cs cluster state with Rb-mediated interactions. The dual-species platform and techniques established in this thesis pave the way toward measurement-based algorithms and real-time feedback control in large-scale quantum systems.
Qubits encoded in the electronic states of single atoms trapped in arrays of optical tweezers are a promising platform for a universal quantum computer. These qubits can be prepared in a well-defined quantum state, coherently manipulated using a nearresonant driving field, and their state detected with high fidelity. The most promising aspect of this platform is the large scalability, with arrays of up to 6100 qubits demonstrated[62].We present our progress in developing such a system with an array of single 85Rbatoms. We provide an overview of the experimental setup constructed for this purpose. Typically 50 atoms are loaded from a MOT into a 10×10 array of optical tweezers with sub-micrometer waists, with only a single atom present in a tweezer. The occupation of the tweezers is determined using a fluorescence image. We provide a characterisation of the trapping potentials experienced by the atoms. This characterisation is performed by measuring properties of the atoms in the tweezers, allowing for an in situ characterisation. In particular, the trap depth and trap frequencies were characterised. The temperature of the atoms after the initial fluorescence image was determined using the release and recapture technique [101] and the trapping lifetime of the atom was measured. With the ability to prepare, manipulate, and read out the electronic state of the atoms, an array of hyperfine qubits has been created. The qubits are encoded in the hyperfine clock states as |0⟩ := 52S1/2 |F = 2,mF = 0⟩ and |1⟩ := 52S1/2 |F = 3,mF = 0⟩. These long-lived first-order Zeeman shift insensitive states exhibit good coherence times, which we have characterized as T1=205 ± 3 ms , T2* = 2.01 ± 0.02 ms, andT2 echo = 67.1 ± 0.1 ms. State preparation is achieved by repetitions of optical and microwave pulses, to which the |0⟩ state is dark, allowing for population to accumulate in this state. The coherent evolution of the qubits have been performed using 3.035 GHz microwave radiation. The antenna used to produce this radiation is a home-built fullwave loop antenna. The antenna has allowed for addressing the qubits with Rabi frequencies up to Ω/2π ≈ 160 kHz. We have implemented the single-qubit Clifford gates using the global microwave drive. We determine using randomized benchmarking an166 Summary average gate fidelity of 0.99949(3), limited by Rabi frequency inhomogeneity over the array. To combat this fidelity limitation, we repeated the randomized benchmarking using the pulse length error robust SCROFULOUS pulses [135], which resulted in an increased gate fidelity of 0.999653(5). As a further extension of the capabilities of the system, we demonstrated a preliminary implementation of addressing a single atom int he array by applying a local Rz rotation to the selected qubit using a Stark shifting laser. The high level of control of the microwave radiation has allowed for an experimental verification of control noise-fidelity relations proposed by [115]. We have found good agreement between the experimentally measured fidelities and the proposed analytical relations developed using the stochastic Schrödinger equation. As a preliminary step towards implementing a two-qubit gate, we have performed coherent excitation of the |1⟩ state to the |r ⟩ :=602S1/2 |mJ = −1/2> Rydberg state using an off-resonant two-photon excitation. The low contrast of the Rabi oscillations on the |1⟩↔|r ⟩ transition was investigated using a simple Lindblad master equation based model. The largest contributors to the reduced contrast is SPAM error, intermediate state scattering and laser phase noise. Since Rydberg atoms interact via the van der Waals interaction, the spacing between atoms must be deterministically controlled. For this purpose, we have used an additional optical tweezer which can be dynamically moved using an acousto-optic deflector to rearrange the stochastically filled array into a desired configuration. By placing 2 atoms a distance ≈ 5 μm apart, we have demonstrated the p2 enhancement of the Rabi oscillation on the |1⟩↔|r ⟩ transition, a required first step towards implementing an entangling gate between the hyperfine qubits. To extend the temperature-limited T2* coherence time, we have implemented Λ-enhanced gray molasses cooling. We have opted to perform this cooling on the D2line as it is experimentally convenient to use this transition. Because using this transition for this purpose has not been reported in this isotope of Rb, we studied the efficacy of this cooling scheme under these circumstances. The reduced excited state hyperfine splitting of 85Rb compared to 87Rb has allowed for the study of the efficacy of this technique in the presence of additional transitions that may inhibit the cooling performance. Despite the challenges of the smaller hyperfine splitting, we have cooled the atoms to4.0±0.2 μK. This additional cooling is partially negated by the heating from the qubit state preparation procedure, but the additional cooling has allowed for the average T2*to be extended from ⟨T2*⟩ = 3.4 ± 0.1 ms to ⟨T2*⟩ = 5.3 ± 0.2 ms.
Neutral atom quantum computing utilizes laser-trapped neutral atoms as qubits and realizes quantum logic gate operations through Rydberg-state interactions. In recent years, it has become one of the most vibrant directions in quantum computing hardware. This paper systematically reviews the working principles of neutral-atom quantum computers, including qubit encoding, atom trapping and manipulation, Rydberg states and interactions, the Rydberg blockade quantum gate mechanism, and atom rearrangement with reconfigurable architectures. The mainstream technical routes are surveyed, represented by optical tweezer arrays combined with Rydberg interactions, optical lattice schemes, and dipole trap arrays. A panoramic review is provided of domestic and international research progress from theoretical foundations in 2000 to the latest achievements in 2026, including thousand-qubit-scale systems, logical qubits, and quantum error correction experiments. Key breakthroughs are highlighted, such as the 6100-atom qubit array, continuous operation of a 3000-qubit system, quantum simulation of the Kitaev honeycomb model, toric code error correction demonstrations, encoding rates exceeding 1/2, and fault-tolerant architectures. The core bottlenecks are analyzed in depth, including the scalability--fidelity trade-off, engineering implementation of quantum error correction, atom loss and mid-circuit replenishment, laser system industrialization, control electronics scalability, and long-distance quantum interconnection. This paper aims to provide a systematic reference for academic research and technological development in this field.
Quantum error correction (QEC) [1,2] is essential for the realization of large-scale quantum computers [3,4]. However, due to the complexity of operating on the encoded ‘logical’ qubits [5,6], understanding the physical principles for building fault-tolerant quantum devices and combining them into efficient architectures is an outstanding scientific challenge. Here we utilize reconfigurable arrays of up to 448 neutral atoms to implement the key elements of a universal, fault-tolerant quantum processing architecture and experimentally explore their underlying working mechanisms. We first employ surface codes to study how repeated QEC suppresses errors [6,7], demonstrating 2.14(13)x below-threshold performance in a four-round characterization circuit by leveraging atom loss detection and machine learning decoding [8,9]. We then investigate logical entanglement using transversal gates and lattice surgery [10–12], and extend it to universal logic through transversal teleportation with 3D [[15,1,3]] codes [13,14], enabling arbitrary-angle synthesis with polylogarithmic overhead [5,15]. Finally, we develop mid-circuit qubit re-use [16], increasing experimental cycle rates by two orders of magnitude and enabling deep-circuit protocols with dozens of logical qubits and hundreds of logical teleportations [17–20] with [[7,1,3]] and high-rate [[16,6,4]] codes while maintaining constant internal entropy. Our experiments reveal key principles for efficient architecture design, involving the interplay between quantum logic & entropy removal, judiciously using physical entanglement in logic gates & magic state generation, and leveraging teleportations for universality & physical qubit reset. These results establish foundations for scalable, universal error-corrected processing and its practical implementation with neutral atom systems.
Subsystem readout during a quantum process, or mid-circuit measurement, is crucial for error correction in quantum computation, simulation, and metrology. Ideal mid-circuit measurement should be faster than the decoherence of the system, high-fidelity, and nondestructive to the unmeasured qubits. Here, we use a strongly coupled optical cavity to read out the state of a single tweezer-trapped ^{87}Rb atom within a small tweezer array. Measuring either atomic fluorescence or the transmission of light through the cavity, we detect both the presence and the state of an atom in the tweezer, within only tens of microseconds, with state preparation and measurement infidelities of roughly 0.5% and atom loss probabilities of around 1%. Using a two-tweezer system, we find measurement on one atom within the cavity causes no observable hyperfine-state decoherence on a second atom located tens of microns from the cavity volume. This high-fidelity mid-circuit readout method is a substantial step toward quantum error correction in neutral atom arrays.